1. Field of the Invention
The present invention relates to an intervertebral implant including a spacer for being applied between two spinous processes of two vertebrae of the spine.
2. Discussion of Related Art
Well-known intervertebral implants comprise a spacer for inserting between the spinous processes which extend the posterior portions of vertebrae in order to limit and control relative displacement of the vertebrae relative to one another. Such implants are generally installed on the spine of a patient suffering from a degenerative pathology of the spine in which the vertebrae run the risk of approaching one another and, for example, of compressing the roots of nerves. A first category of spacers has been devised that are entirely rigid and made as a single piece presenting two opposite ends suitable for being connected respectively to two contiguous spinous processes by link means. Thus, when the spine is extended, for example, the extent to which the posterior portions of two vertebrae can move towards each other is limited by the spacer against which the spinous processes come to bear; when the spine is bent forwards, the spinous processes are held relative to each other by the link means. Nevertheless, such a rigid spacer does not reproduce accurately the real physiological conditions under which relative movement between vertebrae is limited. To mitigate that problem, a second category of spacers has been devised, made of material that is elastically deformable, thus making it possible to reproduce as accurately as possible the conditions for controlled relative displacement of vertebrae during movements of the spine. As a result, the forces tending to push vertebrae apart increase as they move towards each other.
Nevertheless, the elastically deformable materials used that are suitable for being compressed in order to limit the extent to which vertebrae can move towards each other deform in the longitudinal direction in a manner that is too great compared with the displacements of the vertebrae of a normal person.